It is important to have relatively precise information about the velocity of air relative to the airborne aircraft. Pitot tubes are widely used for this purpose and determine the relative velocity of the air by measuring air pressures.
Pitot tubes are oriented towards the airflow to measure a dynamic pressure. In order to ensure satisfactory operation, Pitot tubes have to be regularly maintained and protected from external impacts from materials such as ice, volcano ash, birds or insects.
Also, extensive calibrations and corrections are necessary in order to enable the required measurement precision. Failures of Pitot tubes have had fatal aircraft accidents as a consequence.
Recently optical methods have been developed for measuring the relative velocity of airflow.